1. Field of the Invention
The present invention relates to an image display device that displays medical images representing a photographed subject.
2. Description of the Related Art
In the medical field, it is widely practiced to utilize medical images representing a photographed internal body of a subject by using radiation or the like for the diagnosis of symptoms of the subject. Utilizing the medical images for the diagnosis enables a person in the medical field to grasp the stages of symptoms of the subject or the like without causing external damage to the subject and obtain necessary information to determine treatment plans or the like.
Further, in recent years, such devices as CR (Computed Radiography) for obtaining digitalized medical images by using radiation, CT (Computerized Tomography) for obtaining tomograms of the subject by using radiography, and MRI (Magnetic Resonance Imaging) for obtaining tomograms of the subject by using strong magnetic fields are becoming widely used, and digitalized medical images are becoming commonly used instead of medical images using conventional X-ray films or the like. With the digitalization of medical images, it is possible to collectively manage the medical images together with digitalized medical records of the subject, and to share the medical images and the records among hospitals or the like via network. Thus, even though a clinic or a hospital where the subject receives treatment is changed, the medical images and the medical records showing the past history of disease of the subject can be utilized.
Also, with the digitalization of medical images, applying image processing on the medical images becomes easy, thereby multiple medical images of an identical subject photographed at different times are displayed arranged side-by-side on a monitor, and an image of a region-of-interest suspected as a lesion on the medical images is cut out to be enlarged on the monitor. However, even if the medical images are displayed arranged side-by-side or the image of the region-of-interest is enlarged, there is a problem that it is hard to recognize variations when increase and decrease of the lesion is little.
In this regard, Japanese Patent Application Publication (JP-AP) No. 2004-96417 describes a technique of displaying a difference image representing a difference between medical images on a monitor. By checking the difference image displayed on the monitor, a doctor and a subject can easily confirm the degree of increase and decrease of a lesion.
However, it is very difficult to photograph a subject in the exact same position at each different time. Thus, in the technique described in JP-AP No. 2004-96417, there is a problem that a slight displacement in the positions of the subject between the medical images appears on the difference image, thereby a difference caused by variations of the lesion and a difference caused by the position-displacement are mixed on the difference image.
Also, Japanese Patent Application Publication (JP-AP) No. 6-175245 discloses a method of matching positions between multiple images. Creating a difference image after matching positions between the multiple images with the use of the technique described in JP-AP No. 6-175245, the inconvenience of position-displacement appearance on the difference image can be reduced.
However, even with application of the techniques described in JP-AP No. 2004-96417 and JP-AP No. 6-175245, a slight displacement in postures of a subject and variations in the body size of the subject, which are hard to be corrected only through position-displacement correction processing, appear on a difference image. As a result, on the difference image, not only variations of the lesion, but also differences due to various kinds of causes are mixed. Therefore, it is hard to recognize variations of the lesion by checking the difference image or comparing the medical images.